This invention relates to a method for manufacturing an automotive component such as a bumper beam, body panel or interior trim piece. In particular, this invention relates to a method for manufacturing an automotive component which has reinforcement ribs on the back side and a visibly smooth front or outer surface.
Many automotive components are manufactured with structural ribs on the back side. Examples of such parts include decorative bumpers, body panels and interior trim pieces. When structural ribs are molded onto the back side of a part, it is common that the front surface will develop depressions or sink marks at the rib locations. On a visible or class A surface, sink marks are highly undesirable.
It is possible to mold a part to avoid sink marks. The thickness of the rib structures is reduced to minimize sink marks. However, additional brackets or parts are required in order to improve the strength of the part.
Alternatively, the sink marks can be covered by other parts. For example, a facia is used to cover a bumper beam. The facia will have small ribs in order to prevent sink marks and will cover the bumper beam which will have sink marks.
The disadvantages of the prior art may be overcome by providing a method for manufacturing an automotive component, such as a bumper beam, body panel or interior trim piece, with structural ribs and without visible sink marks.
According to one aspect of the invention, there is provided a mold, comprising of mold halves wherein at least one mold half has at least one section which is movable between a first injection position and an expanded second injection position. At the first stage, the mold halves are closed and the section is in the first injection position to present a first cavity for forming a primary part having structural ribs on the back side. Molten material is injected into the first cavity. The section is then retracted from the first injection position to the expanded second injection position defining a second cavity between the molded primary part and the section. Molten material is injected into the second cavity to overmold the front surface of the part covering any sink marks which may have developed during the first injection step. Once the part is sufficiently solidified, the mold is opened and then the part is ejected.